WO2012082026A1

WO2012082026A1 - Method and device comprising two feeding screws for continuously operating a pyrolysis reactor

Info

Publication number: WO2012082026A1
Application number: PCT/SE2010/051372
Authority: WO
Inventors: Lars Johansson
Original assignee: Lars Johansson
Priority date: 2010-12-13
Filing date: 2010-12-13
Publication date: 2012-06-21

Abstract

The present invention relates to a method for pyrolytic decomposition of a material in a pyrolysis reactor (100) intended for continuous operation comprising supplying the material towards the pyrolysis reactor (100), pyrolysing the in the pyrolysis reactor in the absence of air, removing gas and residual products resulting from the pyrolysis process. The supplying step comprises: feeding the material through a first feeding means comprising a first feeding conveyor screw (3) arranged in a first supply channel and driven by a first driving motor (2) towards a second feeding means (6) comprising a second feeding screw conveyer unit (7) driven by a second driving motor (4). The first feeding channel is slanted upwards from an input towards the second feeding channel. The speed of the second conveyor unit driven by the second motor (4) is preset depending on the material to be pyrolysed. A material compression related feature in the second feeding means (6) is detected by a sensing arrangement (60), and detected current values are used for controlling the first driving motor (2) to obtain a substantially constant or desired degree of compression in the second feeding means (6).

Description

Title :

METHOD AND DEVICE COMPRISING TWO FEEDING SCREWS FOR CONTINUOUSLY OPERATING A

PYROLYSIS REACTOR

TECHNICAL FIELD

The present invention relates to a method for pyrolytic decomposition in a pyrolysis reactor intended for continuous operation comprising, supplying the material towards the pyrolysis reactor, pyrolysing the material in a pyrolytic process in the pyrolysis reactor in the absence of air, removing gas released by the pyrolysis process, and removing residual products resulting from the pyrolytic decomposition, such as slag. It also relates to a corresponding pyrolysis arrangement .

BACKGROUND

Gas generators for segregating combustible material are well known, not least in the form used previously and they are still used in certain plants for the production of town gas, for example. The basic concept itself is the same, namely anaerobic segregation at increased temperature, and the handling of released gas and residual products. However, so far, no one has succeeded in providing a pyrolysis reactor which actually does operate continuously. For the unfortunate case that air or free oxygen unintentionally comes into contact with a material undergoing pyrolysis, this unavoidably results in an explosive fire. Basic physics teaches that three conditions need to be met for combustion to take place: firstly that access to a combustible material is provided, secondly that the temperature at which the combustible material burns is reached, and thirdly that there is access to free oxygen in the required quantity. In a pyrolysis reactor or gas generator conditions must thus be created for an anaerobic process, more precisely a process in which all the conditions for combustion exist, except for access to free oxygen. Because no one has succeeded in producing a gas generator for continuous pyrolysis of combustible material, designs that have worked so far are characterised in that they must be operated in batches, i.e. a pyrolysis reactor is loaded with a set of pyrolysable material which is then heated under oxygen-free conditions at the same time that the gas released during the process is handled. During the pyrolysis process the pyrolysis reactor is hermetically sealed to avoid explosive processes. Prolonged cooling is thereafter required to bring down the temperature in the gas generator to such a level that the residues remaining after pyrolysis do not spontaneously ignite when free oxygen penetrates as the pyrolysis reactor is being opened. This is not, nor has it ever been, a particularly good process, not least because it involves extensive handling relating to loading, heating and cooling. It is also not energy effective.

SUMMARY

It is therefore an objective of the present invention to provide a method and a device respectively as initially referred to through which the above mentioned problems are overcome and which is efficient and reliable. It is particularly an object to provide a method and an arrangement respectively through which it becomes possible to guarantee that neither oxygen nor air is fed into the pyrolysis reactor whilst the continuous pyrolysis process is taking place. Particularly it is an object to provide a device and a method respectively which can be used for different materials and which can handle irregularities in the material and/or in temperature .

Therefore a material and a device respectively is provided which has the characterision of the respective independent claims. Advantageous embodiments are given by the appended subclaims. Through sensing a compression related feature, e.g. the pressure against the walls, e.g. an upper wall of the second supply or feeding channel (in the following called channel even through it may be a pipe or a duct or similar) , and using a current value of the sensed feature, to control the driving speed or the rotation (frequency) of the second motor, this can be continuously controlled and an even, desired level of compression can be obtained (in the second feeding channel) irrespectively of any occasional, expected or unexpected, irregularities in the feeding of material, variations in material/material density etc.

The operating or driving speed or rotation frequency of the second motor can be preset to a given value depending on material properties, e.g. density etc. In an advantageous embodiment it is also set depending on operation temperature and depending on capacity of the pyrolysis arrangement (e.g. reactor and feeding means) . During normal operation the speed/rotation of the second motor is set to a constant value whereas the speed/rotation of the first motor (or motors) is regulated depending on the measured (current) value of the compression (density) or the pressure exerted e.g. on a wall as discussed above. A computer controlled control means connected to the detecting means continuously or with a given frequency receives information concerning a measured quantity and controls the first motor (e.g. by means of a speed regulator, switches etc.) . It may, at detection of preset alarm levels as far as the measured quantity is concerned, (e.g. too low or too high pressure) switch off the second motor. The control function is also adapted to switch it on after a stop, lowering the speed, and particularly after a stop, gradually increasing the speed. Normally an even compression is desired, e.g. a given degree of compression. It is apparent that for example since the density of tyres or rubber differs a lot from e.g. that of foam or similar, if there is a slight (unintentional or intentional) mixture of materials, this will have considerable effects on the compression or pressure related features.

It can particularly be assumed that no object can enter the pyrolysis reactor by having a satisfactory, desired and even, constant, degree of compression. Preferably, if the second screw conveyor unit comprises two conveyor screws, the detecting means is arranged in the upper part of the second channel or pipe, between the two conveyor screws, to obtain measured values which are not affected by the screws, e.g. by scrapping material in the direct vicinity of the detector. If there are more than two conveyor screws arranged in parallel in the second conveyor unit, a detector or a sensor may be arranged between the or each pair of conveyor screws. Then two or more current values may be obtained and a mean value or an optimized value may be provided which enables an even more accurate control of the first motor.

Preferably a (each) detector is arranged opposite to, and above the "inlet" from the first conveyor. Also if there is only one second conveyor or if there are two second conveyor screws, one or more detectors may be used to assure that extremely accurate values are obtained. Particularly a constant compression is obtained all the time, and it is aimed at having the second feeding means, and the screw threads, full with material all the time.

According to the invention a compression zone (in the second channel) where there is no oxygen whatsoever is obtained.

The material intended for pyrolysis is fed by means of the first screw conveyor to a conveyor unit which in an advantageous embodiment comprises two screw conveyors rotating in the same direction. Alternatively the conveyor unit comprises three or more screw conveyors, which preferably are arranged in parallel in a tube or channel. According to the invention the material intended for pyrolysis can be compressed so that all the air and oxygen bound by it is pressed out. The compression can be even more favoured and the propulsion of the material even more simplified because both, or all of, the conveyor screws of the conveyor unit rotate in the same direction. It should be clear that the screw conveyor or conveyors of the second unit may be driven at a higher speed that the first screw conveyor, at least occasionally, since the result of the measurements may lead to a lowering of the speed, or even a switch off of the first motor, and hence the first screw conveyor (s). In normal, or steady-state operation the screw (s) of the first conveyor is in an advantageous embodiment driven at a higher or equal speed than the second screw conveyor (s), or so driven that the flow of material is higher per unit of time than for each of two or more second screws.

According to a further embodiment the second conveyor unit comprises two screw conveyors that are driven at different speeds. This enables a higher degree of compacting to be achieved than otherwise, thus providing even better sealing than would otherwise be the case. In this particular case the screw conveyor in the conveyor unit that has the higher speed is nevertheless, preferably, or most of the time, driven at a speed that is lower than the speed of the first screw conveyor .

This further reduces the risk of pockets of suction from occurring, which could otherwise, at least technically, cause air to be sucked into the pyrolysis chamber under a pressure that is lower than the surrounding atmospheric pressure.

During the process of starting up a continuous pyrolysis process of the type described in the introduction, material is fed, according to a further embodiment of the invention, to an openable shutter at the feed-in end of the pyrolysis reactor during an introductory phase of the continuous feeding of material. The shutter favours the build-up of a plug of pyrolysable material translatable by means of the screw conveyors and, after an introductory phase, it can be kept open as long as the reactor is being driven and material is fed continuously and it thus has no other function than as a shutter during the reactor heating process.

In accordance with still another embodiment a gas can be supplied which is lighter than air or oxygen, preferably nitrogen, to the upper section of the supply means (e.g. the second feeding channel) , so that as a result of the mass ratio between the gases, all air and any free oxygen can be successively forced out of the supply means in a direction opposite to the conveying direction of the pyrolysable material. Since the first feeding channel or pipe is arranged sloping upwards, i.e. inclined, the supply means will operate approximately in the same way as a traditional water lock, but instead with nitrogen gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be further described in a non-limiting manner, and with reference to the attached drawings, in which: Fig. 1 schematically shows a cross-sectional side view of a pyrolysis reactor arrangement according to one embodiment,

Fig. 2 schematically shows the reactor arrangement of Fig. 1 from above, and

Fig. 3 shows a scrubber with an inlet for gas from the pyrolysis reactor. DETAILED DESCRIPTION

Fig. 1 schematically illustrates a pyrolysis arrangement comprising a pyrolysis reactor 100 for continuous operation. It should be noted that the entire pyrolysis reactor 100 is suitably arranged at an angle of inclination of approximately 5° with respect to the horizontal plane. At the feed-in end of the pyrolysis reactor arrangement there is a feed hopper 1 in which material, e.g. fragmented car tyres, is fed down. At the bottom of feed hopper 1 there is a first feeding means comprising a first screw conveyor 3 arranged in a first channel or pipe and driven by a motor 2, which first screw conveyor 3 propels the fragmented material through the channel which is arranged to form an inclination angle of between 10° and 45° with respect to a horizontal ground plane. Around the first feeding means (screw conveyor 3 in channel) there is a preheating device 5 for heating the material to just above 100°C, firstly in order to expel any moisture containing bound oxygen from the material, secondly to soften the material so that it can be compacted more easily. At the upper end of the first feeding means with screw conveyor 3 there are nozzles (not shown) for supplying nitrogen gas which, because it is lighter than both air and oxygen gas, will stratify due to the inclination of the feeding means, so that it will expel any air or oxygen gas present at feed hopper 1.

In addition to the above-mentioned nozzles for nitrogen gas, a second feeding means with a screw conveyor unit 7, driven by at least one motor 4, and with double conveyor screws which are driven in the same direction of rotation, but at a lower speed than feed conveyor screw 3 (when a second conveyor screw has a smaller screw diameter) , is connected to the upper end of first feeding means comprising the first screw conveyor 3 in the first channel. One end 8 of the second feeding means 6 (second screw conveyor unit 7) is so arranged and connected that it is tightly sealed against the surrounding air some distance into a reactor chamber 9, at an end of which is arranged a shutter 10 which is manoeuvrable between a closed and an open position.

The function of shutter 10, upon initiation of a continuous pyrolysis process, is to enable an establishment of an initial press mass of process material from which all the oxygen can be displaced so that it can be removed (driven out) , in the manner described above, to the feed pocket via screw conveyors 3 and 6 respectively. As referred to above, the second screw conveyor unit 7 is followed by a reactor chamber 9, and the press mass falling to the bottom of the chamber will fall out of it onto a slow moving conveyor belt 11. A levelling plough 12 is here arranged in the initial section of belt 11 in order to distribute the press material evenly over the belt 11. During a continuous process a fragment which is to be pyrolysed remains in pyrolysis reactor chamber 9 for approximately 3 minutes, wherein the chamber in a hot zone 13 keeps an essentially constant temperature of approximately 550°C. In roof 14 of hot zone 13 there are heating elements 15, preferably electrically heated elements of the infra-radiation type, which is why, since the heat supplied is of the radiation type, hot zone 13 preferably is demarcated by radiation protection device 16 at the respective ends of hot zone 13. The radiation protection devices are intended primarily to concentrate the heat discharge within the area in hot zone 13 intended therefore. After passage through zone 13 there remains a residual fraction of the material intended for pyrolysis which consists mainly of carbon black which, at the end of the conveyor belt, falls down to a screw conveyor 18 arranged in an outlet duct 17 for conveying to an oxygen sealed intermediate store (not shown) , which is emptied instantaneously if necessary. A certain proportion of the material intended for pyrolysis will unavoidably behave in a manner that is not desirable and will either drop down alongside belt 11, or will adhere to this and will therefore possibly spontaneously fall off the same at a later stage, whilst the material is located along the underside of the belt. Depending on which is the position where this takes place, it is either handled in the intended manner and drops out as carbon black onto duct 17, or it drops onto the underside of belt 11 in the form of residual material. For this likely eventuality a further screw conveyor 18 is arranged at the bottom of reactor chamber 9, which screw feeds such material and any liquid fraction to an outlet 19 arranged at the feed-in end of reactor chamber 9, from which a feed screw 20 feeds this material to an oxygen-sealed intermediate storage which, like the intermediate storage mentioned above, is instantaneously emptied if required.

A detecting device 60, e.g. a pressure sensor, is arranged in the upper part, e.g. at the upper wall of the channel or pipe of the second feeding means comprising (here) a screw conveyor unit 7 in the region where the first feeding means and the second feeding means are joined, i.e. an end of the first channel enters the second channel, where the material conveyed by the first screw conveyer enters the second channel, and from where it will be conveyed by the second screw conveyor unit 7 for feeding into the pyrolysis reactor chamber 9.

If there are two conveyor screws in the second screw conveyor unit 7, the detector 60 is preferably arranged between (and above) the conveyor screws, see also Fig. 2 very schematically illustrating two second conveyor screws

I 2 and an exemplary location of the detector or sensor 60. In one embodiment the first conveyor screw is longer than the (here) two second conveyor screws

I 2 and has a larger diameter, e.g. 3-10 cm larger (not shown in Fig. 2) than that of the two second conveyor screws. As an illustrative, non-limiting example only, the diameter of the first screw conveyor may be about 140-200 mm or more (or less), e.g. 170 mm, and the diameter of the second conveyor screws may be about 80-160 mm, e.g. 120 mm. It should be pointed out that the dimensions may differ a lot from the exemplifying figures and e.g. be several times larger, but also smaller. It should also be noted that the rotational frequencies of the conveyor screws are low, e.g. in the order of size of 1 rotation in 1-20 seconds and a pressure is hence slowly built up in the supply channel (second feeding channel, cf . where the detector 60 is arranged) .

A main thing is that the amount of oxygen can be minimized, a constant compression be up-held, and any variations automatically handled by means of the control of the first driving motor.

In advantageous embodiments, the second channel or pipe is arranged to have a same inclination with respect to a horizontal plane as the pyrolysis reactor 100 (see e.g. Fig. 1) whereas the second channel forms an angle with the second channel, which it enters from below. Fig. 2 shows a pyrolysis arrangement 100 substantially as in Fig. 1, viewed from above. From the left, the first driving motor 2 for the first conveyor screw 3, followed by feed hopper 1 are shown, then first feeding means (first screw conveyor) 3 surrounded by preheating device 5. The first feeding means with screw conveyor 3 connects to second feeding means 6 with screw conveyor unit 7, which is in turn connects to reactor chamber 9 in the vicinity of a shutter 10 at the outlet end of second screw conveyor unit 7. Connected to the reactor chamber 9 is firstly a gas outlet pipe 21, via which gas released as a result of the pyrolysis process is handled, secondly an outlet duct 17 for carbon black or the like and thirdly an outlet duct 19 for residual material and liquid fraction according to the above description. Ducts 17 and 19 respectively, and pipe 21, are provided with an intermediate storage functionality which may require to be emptied occasionally. This takes place, of course, without giving oxygen or air the opportunity, to get in through the "back door" and disturb the process in the pyrolysis chamber. It can be seen that the detector 60 is arranged above the first screw conveyor 3 and between (and above) two second screw conveyors li, 72. The detector 60 provides measurement results to control means 65 controlling the first motor 2. In Fig. 2 each second screw conveyor 7ι, I2 is driven by a separate motor; it could also have been a common second motor.

The speed of the first screw conveyor is substantially continuously regulated such that an even compression is obtained. It should be clear that the actual speeds depend on the number of screws of a first and a second screw conveyor and the screw diameters and the pitches of the threads.

In some embodiments the first and second screws have the same diameter and/or pitch, in others the pitch and/or diameter is higher or lower in the first screw, the diameters of two or three second screws may be smaller than that of the first screw etc. Figure 3 shows schematically an arrangement 22 which may be described as a liquid lock or scrubber arranged in a tank or container 23, at the inlet of which tank or container gas from reactor chamber 9 is pumped in to maintain a gas pressure inside reactor chamber 9, which corresponds to the atmospheric pressure of the area surrounding the pyrolysis reactor. The gas passes through a pipe 24 down below a liquid surface so that it is released under the surface and is allowed to diffuse out into a collection device at P. The gas in question has a high calorific value and can be used in a number of different applications, e.g. as fuel in gas-driven vehicles such as urban buses. At approximately half the height of container 23 there is a drain tap 25 to enable any products of condensation that can be formed and prevent container 23 from being filled over its width.

Pyrolysis reactor 100 arranged for continuous operation may slope downwards towards the feed-in end. Feed hopper 1 is so large that continuous operation can be maintained without any practical problems. Motor 2 is of such a type that its speed can be varied so that effective compression towards double screw 7 can be guaranteed under all conditions, regardless of the type of material fed in. It is controlled by means of control means 65 (computer controlled) which collects measurement data from detector or sensor 60 and provides a control signal to first driving motor 2 to regulate the speed thereof in dependence of e.g. the detected pressure as discussed above. The speed of the second motor (or motors) 2 is preset depending on material, and optionally also other features, and in an advantageous embodiment the speed of the second motor 2 is lower than that of the first motor unless the first motor has to be temporarily switched off or its speed lowered considerably due to the measured value (e.g. pressure) being too high, also, if there is not enough material (in the second feeding means) it has to be switched off. For effective compression, and to ensure that all moisture is expelled from the material intended for pyrolysis, this material should reach a preheating temperature of 120°C in front of shutter 10 for hot zone 13 of reactor chamber 9. Shutter 10 is here spring loaded to an open position, but is kept closed by a lock (not shown) as long as an oxygen gas detector (not shown) , arranged in the conveyor pipe of second screw conveyor unit 7, indicates that there is oxygen gas in the compression zone of the pipe or in hot zone 13. This oxygen gas detector also controls, by means of a computer (e.g. the control means 65 or another control means) suitable for the purpose and associated software, whether nitrogen gas is to be supplied or not. For example, if a fault occurs in any of the motors 2, 4 driving the screw conveyors, all or some feed-in and heating elements 15 are closed, as is also shutter 10 with positively controlled means (not shown) arranged according to the intended use. Under such conditions it is appropriate to maintain a nitrogen gas atmosphere in the feeding channels (pipes) and reactor chamber 9 until the temperature in it has dropped to such a level that there is no longer a risk for fire in the material intended for pyrolysis. The temperature in hot zone 13, which is maintained by means of heating elements arranged in its upper part or roof, is controlled by thermostats and software in a/the computer so that it is kept at around 550°C +/- 5°. As a result thereof a degassing of material supplied and levelled out by means of plough 12 which is as complete as possible can be obtained as the material passes through hot zone 13. The invention is not limited by the illustrated embodiments but can be varied freely within the scope of the appended claims .

Claims

1. A method for pyrolytic decomposition of a material in a pyrolysis reactor (100) intended for continuous operation comprising the steps of:

supplying the material towards the pyrolysis reactor

(100) ,

pyrolysing the material in a pyrolytic process in the pyrolysis reactor (100) in the absence of air,

removing gas released by the pyrolysis process,

removing residual products, such as slag, resulting from the pyrolytic decomposition,

c h a r a c t e r i z e d i n

that the supplying step comprises:

feeding the material through a first feeding means comprising a first feeding conveyor screw (3) arranged in first supply channel or pipe and driven by a first driving motor (2) towards a second feeding means (6) comprising a second feeding screw conveyer unit (7) arranged in a second feeding channel or pipe and driven by a second driving motor or motors (4), wherein the first feeding channel or pipe is slanted upwards from a material input (1) towards the second feeding channel, by:

setting an operation speed or driving frequency of the second motor (4) depending on the material to be pyrolysed;

sensing or detecting a current value of a material compression related feature in the second feeding means (6) by means of a sensing arrangement (60);

using the detected current value for controlling the first driving motor (2) such that a substantially constant or desired degree of compression is obtained in the second feeding means (6) .

2. A method according to claim 1,

c h a r a c t e r i z e d i n

that the driving speed or rotation frequency at which the second screw (s) is/are driven by the second driving motor (s) (4) is/are lower than the speed at which the first conveyor screw is driven by the first motor (2) .

3. A method according to claim 1 or 2,

c h a r a c t e r i z e d i n

that the controlling or regulating of the first motor (2) comprises at least temporarily switching off the first and second driving motors (2) if a current compression related feature value exceeding or falling below a lower limit is detected, or if it is detected that the amount of material falls below a certain value.

4. A method according to any one of the preceding claims, c h a r a c t e r i z e d i n

that the detecting or sensing means (60) comprises a pressure sensor adapted to detect the pressure exerted in the second feeding means (6) by the compressed material.

5. A method according to claim 4,

c h a r a c t e r i z e d i n

that the detecting step comprises:

detecting the pressure exerted by the compressed material on a wall confining the second feeding means (6), e.g. an upper wall located opposite to an input opening where the material is fed in by the first feeding means (3) or where the first and second feeding means are connected.

6. A method according to any one of claims 1-5,

c h a r a c t e r i z e d i n

that the supplying step comprises feeding the material by means of the first screw conveyor (3) towards the second feeding screw conveyor unit (7) which comprises two or more second conveyor screws arranged in parallel in the second feeding channel or pipe.

7. A method according to claim 6,

c h a r a c t e r i z e d i n

that the screws of the second screw conveyor are driven by the second motor (2) or by the second and a third motor, at different speeds, both speeds at normal operation being lower than the speed with which the first screw conveyor (3) is driven by the first motor (2) .

8. A method according to any one of the preceding claims, c h a r a c t e r i z e d i n

that the material, in an introductory phase of the continuous feed of material for the continuous pyrolysis process, is fed towards a shutter (10) at the feed-in end of the pyrolysis reactor (100) .

9. A method according to any one of the preceding claims, c h a r a c t e r i z e d i n

that the supplying step comprises supplying a gas which is lighter than air or oxygen, preferably nitrogen, in the upper section of the second feeding channel so that, as a result of the mass ratio between nitrogen and air/oxygen, all air and oxygen is successively forced out of the second feeding channel or the second feeding means (6) .

10. A method according to any one of claims 1-10,

c h a r a c t e r i z e d i n

that the sensing or detecting step comprises substantially continuously or at regular, short, time intervals sensing the compression related feature in the second feeding channel to enable a continuous control of the driving frequency or speed of the second motor (2) .

11. A pyrolysis arrangement comprising a pyrolysis reactor (100) adapted to operate continuously, a material input (1), for reception of material to be pyrolised, which is connected to a supply arrangement (2,3,4,5,6,7), a mechanism (21,22,23,24,25) adapted to remove gas released during a pyrolysis process in the pyrolysis reactor and a mechanism (19) for removing residual products, such as slag, generated during the pyrolysis process in the pyrolysis reactor (100), c h a r a c t e r i z e d i n

that the supply arrangement comprises a first feeding means comprising a first screw conveyor (3) arranged in a first feeding channel or pipe and a first motor (2) adapted to drive said first screw conveyor unit (3) ,

that the first feeding channel or pipe is connected to a second feeding means (6) comprising a second feeding channel or pipe in which is arranged a second screw conveyor unit (7) which is adapted to be driven by a second driving motor (4), that the first feeding channel is arranged to slant upwardly from a first end at which it receives material from the material input (1) to an opposite end at which it is connected to, and upwardly opens into, the second feeding channel or pipe, that said second feeding means at its other end is connected to the pyrolysis reactor (100) for input of the material supplied and compressed by means of the supply arrangement, that the speed of the second driving motor (4) motor by which the second screw conveyor unit is driven is adapted to be set depending on one or more characteristics of the material to be pyrolysed, e.g. its density,

that detecting or sensing means (60) are arranged to continuously or with a given frequency sense or detect a value of a compression related feature in the second feeding means (6), and control means (6) adapted to, based on the detected values, control the first driving motor (2) for controlling or regulating the rotational speed of the screw or screws of the first screw conveyor (3) such that a substantially constant or desired degree of compression is obtained in the second feeding means .

12. A pyrolysis arrangement according to claim 11,

c h a r a c t e r i z e d i n

that at normal operation and constant compression the screw or screws of the second screw conveyor unit (7) is/are driven with a constant speed which may be lower than the speed at which the first screw conveyor (3) is driven, at least if the diameter of the respective second screws is smaller than that of the first screw.

13. A pyrolysis arrangement according to claim 11 or 12, c h a r a c t e r i z e d i n

that the detecting or sensing means (60) are connected to the control means (65) which comprise or are connected to a regulator for regulating e.g. the speed or rotation of the first motor, that it is adapted to, at detection of a given predetermined value, alarm value, of the monitored feature, switch off the first motor, at least temporarily.

14. A pyrolysis arrangement according to any one of claims 11- 13,

c h a r a c t e r i z e d i n

that the detecting means (60) are connected to a computer controlled regulator arrangement (65) arranged to increase and decrease the speed of the first motor depending on the value of the detected feature and optionally also on one or more additional features, such as temperature.

15. A pyrolysis arrangement according to any one of claims 11- 14,

c h a r a c t e r i z e d i n

that the detecting means (60) comprises a pressure sensor adapted to sense the pressure exerted on a wall, e.g. in an upper portion or wall, of the second channel or pipe, above a region in which the first channel is connected to, or enters, the second channel.

16. A pyrolysis arrangement according to any one of claims 10- 14,

c h a r a c t e r i z e d i n

that the second feeding means (6) comprises two or more conveyor screws (7) arranged substantially in parallel and driven at a same or at different speeds, at least during initial and normal operation being lower than the speed of said first screw conveyor (3) .

17. A pyrolysis arrangement according to any one of claims 11- 16,

c h a r a c t e r i z e d i n

that it also comprises a shutter (10) arranged at an inner end of the second supply channel ending in a reactor chamber (9) of the pyrolysis reactor (100) and adapted to be manoeuvrable to open and close from the outside of the pyrolysis reactor (100), and towards which shutter (10) the material intended for pyrolysis is to be packed during a start-up process of a continuous period for the pyrolysis reactor (100) .

18. A pyrolysis arrangement according to any one of claims 11- 17,

c h a r a c t e r i z e d i n

that it comprises a pre-heating device (5) arranged around at least part of the first feeding means (3) along the first channel and adapted to dry and soften the material intended for pyrolysis.

19. A pyrolysis arrangement according to claim 18,

c h a r a c t e r i z e d i n

that it comprises oxygen gas detectors arranged in a reactor chamber (9) of the pyrolysis reactor (100) and in the second feeding channel connecting to the reactor, which detectors are connected to the control system (65) or to a separate control system adapted to, if air or oxygen is detected, supply an oxygen expelling or removing gas, e.g. nitrogen gas, to displace and remove the oxygen in an upper section of the second feeding channel.

20. A pyrolysis arrangement according to claim 19,

c h a r a c t e r i z e d i n

that said control system (65) or said separate control system is connected to motion sensors adapted to detect whether the screw conveyors (3; 6) are rotating or not, wherein the said control system is adapted to ensure that the reactor (9) is closed down and an atmosphere consisting mainly of nitrogen gas is maintained in the feeding means (3; 6) comprising conveyors and the reactor chamber (9) as long as pyrolysable material is present therein and the temperature is so high that there is a risk for fire.